Electrophotographic photosensitive members each using an organic material (organic electrophotographic photosensitive members) have started to be mounted on a large number of electrophotographic apparatuses (such as a copying machine and a printer) in recent years. The research and development of a material to be used in an electrophotographic photosensitive member have been vigorously conducted.
The research and development of a charge generation substance typified by a phthalocyanine pigment or an azo pigment have been particularly vigorously conducted. Various proposals concerning a novel compound and the novel crystal form of a pigment have been made with a view to improving sensitivity and durability.
In contrast, at present, research and development concerning a binder resin for a photosensitive layer, in particular, a binder resin for a charge generation layer of a laminated photosensitive layer have not been conducted very vigorously.
Under such present circumstances, for example, JP-A-62-030254 and JP-A-05-045899 each disclose a polyvinyl benzal derivative as a resin having an improving effect on sensitivity and a reducing effect on a residual potential. In addition, JP-A-62-035537 discloses a polyvinyl acetal derivative.
In actuality, however, a commercially available product such as polyvinyl butyral is used in most cases in consideration of coating property and the property with which a charge generation substance is dispersed. Accordingly, the properties of the charge generation substance are not always exerted sufficiently.